AB0025 LOW-DENSITY GRANULOCYTES AND NEUTROPHIL EXTRACELLULAR TRAPS IN INCOMPLETE SYSTEMIC LUPUS ERYTHEMATOSUS
Authors: S. Henning, T. Reimers, B. Doornbos- van der Meer, H. Bootsma, K. De Leeuw, J. Westra
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Systemic lupus erythematosus (SLE) is an autoimmune disease with a complex and only partly understood pathophysiology, while incomplete SLE (iSLE) defines a group of patients with symptoms typical of SLE but not meeting sufficient criteria required for the classification of SLE. Up to 55% of patients with iSLE will eventually develop SLE, but it is unclear which patients are at risk of progression. [1] Neutrophil dysfunction, among which aberrant neutrophil extracellular trap (NET) formation driven by low density granulocytes (LDGs), has been implicated in SLE pathogenesis. [2] However, the role of neutrophil dysfunction in early forms of SLE is still unclear. <h3>Objectives</h3> The aim of this study was to investigate whether LDGs are elevated in the peripheral blood mononuclear cell (PBMC) fraction of iSLE patients, compared to healthy controls (HCs) and SLE patients with quiescent disease (SLEDAI&lt;4). Next to that, we investigated presence of circulating NETs in plasma of iSLE as well as SLE patients and HCs. <h3>Methods</h3> Circulating plasma NETs were measured cross sectionally in 38 iSLE patients, 30 SLE patients with quiescent disease and 12 HCs while LDGs were measured in 18 iSLE patients, 13 SLE patients and 14 HCs. SLE patients were classified according to the Systemic Lupus International Collaborating Clinics (SLICC) criteria. Patients with iSLE had to meet at least one clinical and one immunological criterion but less than four SLICC criteria in total. LDGs (CD14<sup>low</sup>CD15<sup>+</sup>) were measured in freshly isolated PBMCs with flow cytometry as previously described [3] and were expressed as percentage of total PBMCs. Circulating plasma NETs were measured by using a previously validated sandwich enzyme linked immunosorbent assay [4] using a plate coated with an anti-myeloperoxidase antibody. Kruskal-Wallis tests were used to compare LDGs and NETs between groups. In case of significance, Mann-Whitney tests were used for pairwise comparison. A two tailed p-value of ≤ 0.05 was considered statistically significant. <h3>Results</h3> Proportions of LDGs and NET-levels were significantly increased in iSLE patients compared to HCs, as shown in Figure 1. The proportion of LDGs and circulating plasma NETs was similar between SLE and iSLE patients. <h3>Conclusion</h3> Our data shows significantly higher amounts of LDGs and circulating NETs in the iSLE and SLE cohort compared to healthy controls, suggesting that aberrant NET formation and clearance is present in early stages of the disease. In future studies, we aim to investigate the correlation between LDGs, circulating NETs and other immunological parameters, such as complement C3 and C4, and anti-dsDNA levels. <h3>References</h3> [1]Lambers WM, Westra J, Bootsma H, de Leeuw K. From incomplete to complete systemic lupus erythematosus, A review of the predictive serological immune markers. Vol. 51, Seminars in Arthritis and Rheumatism. W.B. Saunders; 2021. p. 43–8. [2]Kaplan MJ. Neutrophils in the pathogenesis and manifestations of SLE. Vol. 7, Nature Reviews Rheumatology. 2011. p. 691–9. [3]Denny MF, Yalavarthi S, Zhao W, Thacker SG, Anderson M, Sandy AR, et al. A distinct subset of proinflammatory neutrophils isolated from patients with systemic lupus erythematosus induces vascular damage and synthesizes type I IFNs. J Immunol. 2010 Mar 15;184(6):3284–97. [4]Matta B, Battaglia J, Barnes BJ. Detection of neutrophil extracellular traps in patient plasma: method development and validation in systemic lupus erythematosus and healthy donors that carry IRF5 genetic risk. Front Immunol. 2022 Jul 26;13:951254. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Svenja Henning: None declared, Tobias Reimers: None declared, Berber Doornbos- van der Meer: None declared, Hendrika Bootsma Speakers bureau: Speaker for Bristol Myers Squibb and Novartis, Consultant of: Consultant for Bristol Myers Squibb, Roche, Novartis, Medimmune, argenX, and Union Chimique Belge, Janssen-Cilag and Sanofi, Grant/research support from: Unrestricted grants from Bristol Myers Squibb and Roche AstraZeneca, Karina de Leeuw Speakers bureau: Astra Zeneca, Consultant of: Astra Zeneca, GSK, Otsuka, Johanna Westra: None declared.